1. Field of the Invention
This invention provides a process for preparing polymers having an inorganic backbone comprising zirconium linked to phosphorus through an oxygen bridge.
2. Description of the Art
A novel class of compounds is known, which compounds may be described as inorganic polymers. These compounds are described in U.S. Pat. Nos. 4,232,146; 4,235,990; 4,235,991; 4,256,872; 4,267,308; 4,276,409; 4,276,410; 4,276,411; 4,298,723; 4,299,943; 4,373,079; 4,384,981; 4,386,013; 4,390,690; 4,429,111; and 4,436,899 which are hereby incorporated by reference. These compounds may be prepared having a layered structure similar to the layered structure of zirconium phosphate. The above patents teach that these novel layered compounds have many uses. However, these layered compounds are sometimes difficult to prepare.
The inorganic polymers are generally prepared by a process which comprises reacting, in an aqueous medium, at least one acid compound, i.e. an organo-substituted, phosphorus atom-containing acid, having the formula ((HO).sub.2 OPO.sub.x).sub.k R wherein k may be either 1 or 2 and, R is an inorganic radical, with at least one tetravalent metal ion (e.g. Zr) to precipitate a solid in which the molar ratio of phosphorus atom to tetravalent metal is about 2 to 1, the phosphorus atom is covalently bonded to R when x equals 0, and R is linked to the phosphorus atom through oxygen when x equals 1.
When R contains hydrophilic groups, e.g. carboxyl, sulfo, etc., the reaction product may not separate as an easy-filterable solid. Thus, centrifuging, etc. may be required to recover the reaction product.
Sulfonated derivatives of the above inorganic polymers have been disclosed as useful acid catalysts in International Application No. PCT/US87/090885 (WO87/06244) published on Oct. 22, 1987. These sulfonated catalysts may be prepared from phosphorus-atom containing acids wherein R contains a sulfo substituent; or an inorganic polymer having a sulfonatable radical may be prepared, separated and subsequently sulfonated. In the first instance, the hydrophilic sulfo group may cause the inorganic polymer to be difficult to separate from the aqueous medium. In the second instance, the multiple steps required are undesirable.
The present invention provides a simplified method for preparing the polymers of the above references. Moreover, the present invention provides a method for preparing said polymers as a precipitate which is easy to separate from the reaction medium. Finally, the present invention provides a method for preparing a sulfonic acid-containing polymer, suitable as an acid catalyst, as a precipitate which is easy to filter from the reaction medium, and which does not require the separation of the polymer from the reaction medium in which it is formed, prior to sulfonation.